1. Field of the Invention
The present invention relates to a circuit for compensating for a vertical distortion of images by modes in a display and, more particularly, to a circuit for compensating for a vertical distortion of images by modes, by varying the pulse width of a horizontal output signal to regulate the compensation position, selectively amplifying the voltage of the position-compensated signal to adjust the compensation size, modulating a vertical output signal varied by modes with the compensated horizontal output signal by using an E-I transformer, and applying the modulated vertical output signal to a vertical deflection coil.
2. Discussion of Related Art
In a monitor used as a display in a computer system, a computer includes a central processing unit (CPU) for processing a received keyboard signal and a video card for processing the output signal of the computer into picture signals R, G and B and for generating horizontal and vertical synchronizing signals H-Sync and V-Sync for processing.
The picture signals and the horizontal and vertical synchronizing signals are transferred to a monitor through a picture signal cable. A microcomputer receives the horizontal and vertical synchronizing signals through the picture signal cable to generate a control signal such as an image adjusting signal and a reference oscillation signal. A control button section generates screen control signals to operate the microcomputer. When a user selects an input signal, the control button section transmits the input signal to the microcomputer. A horizontal/vertical synchronizing output circuit receives the image adjusting signal and the reference oscillation signal generated by the microcomputer to synchronize a raster. A video circuit amplifies the picture signals transferred from the video card. A power supply circuit provides power to the microcomputer, the horizontal/vertical synchronizing output circuit and the video circuit.
The display CRT, connected to the video circuit, has electron guns for projecting the electron beams on a screen. As the electron beams are projected horizontally on the screen, an image is formed according to the concentration of the beams. Since the electric field formed by a deflection yoke deflects the electron beams, external factors affecting the electric field can change the deflection angle of the electron beams. The image displayed on the screen may be distorted by internal or external factors. The image may be formed horizontally or vertically in an unsymmetrical way when the electron beams are abnormally projected by the resistance of the image receiver itself as well as an image rotation effect caused by an external magnetic field. An unbalanced image can also be formed by an excessive current applied to the deflection yoke.
One distortion, called a side pin cushion, can be solved by varying the horizontal deflection output voltage and controlling the horizontal width with a pin cushion compensator. The vertical circuit transfers a sawtooth voltage to an integrating circuit and converts it into a parabolic voltage. The pin cushion compensator modulates the parabolic voltage supplied to the horizontal output circuit to adjust the compensation size and position.
The image can be vertically distorted by the generation of the parabolic waveform from the sawtooth oscillation output signal according to the charging and discharging time constant of an RC combination or by the non-linear characteristics of a transistor. Though applying a non-linear current may compensate for the vertical distortion of images, it is unfortunately not applicable to the earlier systems.